This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Electrostatic interactions are often oversimplified or ignored in the energy functions for NMR structure calculations, because it is difficult to evaluate them reliably without proper description of the dielectric screening by solvent. In light of recent improvements in implicit solvent models, it was showed that simulated annealing refinement in a GB implicit solvent could lead to noticeable improvement in the final protein NMR structures in terms of the backbone dihedral angle distributions and hydrogen bond patterns. However, the impact of implicit solvent is rather small when a sufficient number of experimental restraints exist (such as in the final stage of NMR structure determination).